16-33 Skarn Fluid Evolution through the lenses of Garnets

Session: From Thin Section to Outcrop: Exploration of Undergraduate Research (Posters)

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Critical metals, including the rare earth elements (REE), are important resources that modern society will require more of as technology advances, both for common-place items such as cell phones but also for green energies such as wind and solar power. Understanding the formation of these deposits and finding more domestic deposits is critical to the national economy and transitioning from fossil fuels. Skarn type ore deposits are the result of a body of magma and its associated hydrothermal fluids metasomatizing their carbonate host rocks. Skarns are categorized by the metals that they are most enriched with and include Au-, Cu-, Fe-, Mo-, Pb/Zn-, Sn-, and W-type. The differing dominant metals found in skarns are a product of the geochemistry of the hydrothermal fluid. Many skarns are mined currently for their defining elements (such as W or Zn) while others have been historically mined such as Fe type skarns. Like other historic mining districts such as the Iron Oxide-Apatite deposits of the Adirondacks and elsewhere, these skarns may have an underutilized economic amount of Ge, Ga, In, REEs, or other “modern” critical metals that were previously ignored or unknown at the time of mining. This study aims to analyze hydrothermal fluid composition by looking at the geochemistry of garnets. The REE concentrations in the garnets will be heavily emphasized due to the strong relationship between their concentrations and fluid/wallrock interactions. Another major focus will be the oxidation state of the hydrothermal fluids using trace element analysis. Samples from five different skarns including Fe-type, Pb/Zn-type and W-type skarn systems will be compared in order to observe differences in the hydrothermal fluids between these different subtypes. The garnet samples were collected from the Excelsior and Memphis Mines in New Mexico (Pb/Zn-type), the Flat Creek prospect in Nevada (W-type), the Sulphur Hill mine in New Jersey (Fe-type), and the Cornwall Mine in Pennsylvania (Fe-type). Thin sections were made that were representative of each deposit that had garnet present. Electron microprobe analyses will be done at the American Museum of Natural History followed by laser ablation-inductively coupled plasma mass spectrometry. 

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